Systems and methods for reducing z-thickness and zero-order effects in depth cameras

Abstract

A projection system configured to emit patterned light along a projection optical axis includes: a diffractive optical element configured to perform a collimation function on the light emitted by the light emitter and to perform a pattern generation function to replicate the collimated light in a pattern, the pattern having substantially no collimated zero-order; and a light emitter configured to emit light toward the diffractive optical element, wherein the collimation function is configured to collimate the light emitted from the light emitter, and wherein the pattern generation function is configured to replicate the collimated light to produce the patterned light.

What is claimed is: 
     
       1. A projection system configured to emit patterned light along a projection optical axis, the projection system comprising:
 a diffractive optical element configured to perform a collimation function and to perform a pattern generation function; and 
 a light emitter comprising a semiconductor laser diode configured to emit uncollimated light toward the diffractive optical element, 
 wherein the collimation function is configured to collimate the light emitted from the light emitter, and 
 wherein the pattern generation function is configured to replicate the collimated light to produce the patterned light, the patterned light having substantially no collimated zero-order. 
 
     
     
       2. The projection system of  claim 1 , further comprising a housing enclosing the light emitter and the diffractive optical element, the housing having an opening to expose the diffractive optical element. 
     
     
       3. The projection system of  claim 2 , wherein there is no packaging material between the light emitter and housing. 
     
     
       4. The projection system of  claim 2 , wherein the projection system has a thickness along the projection optical axis less than or equal to 3.5 mm. 
     
     
       5. The projection system of  claim 1 , wherein the diffractive optical element has a first facet and a second facet,
 wherein the first facet is configured to perform the collimation function, and 
 wherein the second facet is configured to perform the pattern generation function. 
 
     
     
       6. The projection system of  claim 1 , wherein the diffractive optical element has an optically functional facet configured to perform both the collimation function and the pattern generation function. 
     
     
       7. The projection system of  claim 1 , wherein a length of an optical path from the light emitter to the diffractive optical element is greater than or equal to 1 mm. 
     
     
       8. The projection system of  claim 1 , wherein the light emitter is configured to emit light along a direction non-coaxial to the projection optical axis, and
 wherein the projection system further comprises a micro-mirror arranged to direct the light emitted by the light emitter in the direction of the projection optical axis. 
 
     
     
       9. The projection system of  claim 8 , wherein the light emitter is configured to emit light along a direction orthogonal to the projection optical axis. 
     
     
       10. A depth camera system comprising:
 a projection system configured to emit patterned light along a projection optical axis, the projection system comprising:
 a diffractive optical element configured to perform a collimation function and to perform a pattern generation function; and 
 a light emitter configured to emit light toward the diffractive optical element, 
 wherein the collimation function is configured to supply the pattern generation function with a collimated beam, and 
 wherein the pattern generation function is configured to replicate the collimated beam to produce the patterned light, the patterned light having substantially no collimated zero-order; 
 
 a first image sensor; 
 a second image sensor; and 
 a processor coupled to the first image sensor, the second image sensor, the projection system, and memory, the memory storing instructions that, when executed by the processor, cause the processor to:
 control the projection system to emit the pattern onto a scene; 
 control the first image sensor and the second image sensor to capture a first image and a second image, the first image and the second image being captured substantially simultaneously; 
 process the first image and the second image; and 
 generate a depth map based on the first image and the second image. 
 
 
     
     
       11. The depth camera system of  claim 10 , further comprising a housing enclosing the light emitter and the diffractive optical element, the housing having an opening to expose the diffractive optical element. 
     
     
       12. The depth camera system of  claim 11 , wherein there is no packaging material between the light emitter and housing. 
     
     
       13. The depth camera system of  claim 11 , wherein the housing has a thickness along the projection optical axis less than or equal to 3.5 mm. 
     
     
       14. The depth camera system of  claim 10 , wherein a length of an optical path from the light emitter to the diffractive optical element is greater than or equal to 1 mm. 
     
     
       15. The depth camera system of  claim 10 , wherein the light emitter is configured to emit light along a direction non-parallel to the projection optical axis, and
 wherein the projection system further comprises a micro-mirror arranged to reflect the light emitted by the light emitter in the direction of the projection optical axis. 
 
     
     
       16. The depth camera system of  claim 15 , wherein the light emitter is configured to emit light along a direction orthogonal to the projection optical axis. 
     
     
       17. The depth camera system of  claim 10 , wherein the diffractive optical element has a first facet and a second facet,
 wherein the first facet is configured to perform the collimation function, and 
 wherein the second facet is configured to perform the pattern generation function. 
 
     
     
       18. The depth camera system of  claim 10 , wherein the diffractive optical element has an optically functional facet configured to perform both the collimation function and the pattern generation function. 
     
     
       19. A method for projecting a pattern onto a scene along a projection optical axis, the method comprising:
 applying power to a light emitter comprising a semiconductor laser diode to emit uncollimated light along a first direction, the first direction being non-coaxial with the projection optical axis; 
 directing the emitted light from the first direction toward the projection optical axis; 
 collimating the emitted light; and 
 replicating the collimated emitted light into the pattern, the pattern having substantially no collimated zero-order. 
 
     
     
       20. The method of  claim 19 , wherein the collimating the emitted light and the replicating the collimated emitted light into the pattern are performed by a single diffractive optical element. 
     
     
       21. The method of  claim 20 , wherein the single diffractive optical element has a first facet and a second facet,
 wherein the first facet is configured to collimate the emitted light, and 
 wherein the second facet is configured to replicate the collimated light into the pattern. 
 
     
     
       22. The method of  claim 20 , wherein the single diffractive optical element has one optically functional facet configured to both collimate the emitted light and replicate the collimated light into the pattern.